1. Field of the Invention
The present invention relates to a method and an apparatus for synthesizing urea which synthesize urea by using ammonia and carbon dioxide as raw materials.
2. Background of the Invention
In a urea manufacturing plant, it is important to grasp the operating condition of the plant although there are differences in urea synthesis conditions, such as the urea synthesizing pressure, the urea synthesizing temperature, N/C (the mole ratio of an ammonia component to a carbon dioxide component) and H/C (the mole ratio of a water component to a carbon dioxide component). In particular, N/C is an important parameter for the operation of a urea synthesizing plant and, therefore, it is useful to grasp N/C.
For example, Patent Document 1 discloses measuring the density of a urea synthesis solution in real time at the outlet of a urea synthesizing zone and determining the value of N/C of the synthesis solution from the value of obtained density.
Patent Document 2 describes measuring the compositions of various streams of a urea synthesizing process by use of ultrasonic waves.
Patent Document 3 describes finding the compositions of aqueous solutions of NH3 and CO2 on the basis of measured values of concentration and saturation temperature and using a vibration type densimeter for this concentration measurement.
Patent Document 1: Japanese Patent No. 3270700
Patent Document 2: International Publication WO 01/30748A1
Patent Document 3: Japanese Patent Laid-Open No. 59-133451